The invention relates to an anesthetic machine.
A distinction is made in medical technology between anesthetic machines and ventilation systems.
Pure ventilation systems have been disclosed, for example, in the form of respiratory support machines as described, for example, in DE 38 20 043 A1, DE 37 12 389 A1 or EP 0 112 979 B1. Ventilation machines or respiratory support machines are used to ventilate patients before or after an operation in cases where the patient's own ability to breathe is insufficient.
By contrast, an anesthetic machine is used for the specific treatment of the patient during an operation. In the case of major surgical interventions, the anesthesia is, as a rule, carried out as so-called inhalation anesthesia. In this case, the patient is supplied by an anesthetic machine with the anesthetic gas mixture which is composed of oxygen, laughing gas and a vaporized anesthetic. At the same time, a ventilation is carried out. An anesthetic/ventilation machine is described, for example, in EP 0 058 706 B1.
The prior art relevant to the present invention is explained in detail in FIGS. 6 to 13 to improve understanding hereinafter.
Description of known anesthetic machines with various operating techniques:
As depicted in FIGS. 6 to 8, a known anesthetic machine 1 is essentially composed of three main groups, namely an anesthetic apparatus 2, a ventilation part 3 and an anesthetic system 4. The anesthetic apparatus 2 with a high-pressure gas supply is used to produce a fresh gas flow 5, i.e. an anesthetic gas mixture composed of oxygen, laughing gas and the anesthetic agent. The fresh gas 5 is passed continuously or intermittently into the anesthetic system 4.
The anesthetic system 4 represents the central functional unit of an anesthetic machine with which the actual gas exchange between the machine and the patient is brought about. Depending on the degree of unconsciousness, i.e. the depth of anesthesia, the gas exchange is achieved by the patient in the form of spontaneous breathing or, if spontaneous breathing ceases, by a mechanical or manual ventilation. In this case the ventilation takes place by the additional ventilation part 3.
The anesthetic systems 4 in use at present can be differentiated, depending on the reuse of the gas which is exhaled by the patient 6 and returned to the anesthetic system, into three different basic types which are depicted in FIGS. 6 to 8.
In the "half-open anesthetic system" depicted in FIG. 6, the gas which is exhaled and flows from the patient 6 back into the anesthetic system 4 through line 7 is not reused but completely removed from the system through the anesthetic gas extractor 8. The amount of gas (respiratory gas 9) required by the patient must be supplied to the anesthetic system 4 as fresh gas 5 from the anesthetic apparatus 2 via supply line 10. The gas supply line 10 is called the inspiratory branch and the gas removal line 7 is called the expiratory branch.
In the so-called "half-closed anesthetic system" depicted in FIG. 7, part of the exhaled gas is reused, i.e. the amount of gas (=tidal volume) supplied for inspiration by the patient consists partly of previously exhaled expiratory gas and only partly of fresh gas. A circulation 11 for this purpose is drawn as dotted line in FIG. 7, i.e. the expiratory gas from the expiration line 7 goes in one part to the anesthetic gas extractor 8 and in the other part (arrow 12) back to the inspiratory branch 10. This use of the expiratory gas makes it possible to achieve a considerable saving of fresh gas and simultaneously a conditioning of the inspiratory respiratory gas. The conditioning of the respiratory gas 9 in this case takes place by mixing the fresh gas 5 with the expiratory gas which has 100% humidity and a temperature of 37 degrees Celsius. The conditioning accordingly results in a warming and a moistening of the inspiratory respiratory gas. The smaller requirement for fresh gas 5 also makes an impact in terms of costs.
In the so-called "closed anesthetic system" depicted in FIG. 8, the expired respiratory gas 9' in the expiration line 7 is completely collected in the anesthetic system 4 and returned to the patient 6 at the next inspiration. This is depicted by the closed circulation 11 in FIG. 8, i.e. an anesthetic gas extractor is completely absent. The fresh gas flow 5 which is required is minimal in this system shown in FIG. 8 because it is necessary to supply only the oxygen used by the patient and the stored laughing gas and anesthetic agent. The fresh gas flow 5 is accordingly minimal, which also brings about low environmental pollution by the anesthetic gases due to absence of an anesthetic gas extractor. At the same time, optimal conditioning, i.e. warming and moistening, of the inspiratory respiratory gas 9 is achieved.
With all the anesthetic systems shown in FIGS. 6 to 8, artificial ventilation by the ventilation apparatus 3 is necessary, for example during an operation, because the patient's own respiratory system is switched off because of the anesthesia. In this case, the respiratory gas is supplied to the patient in the inspiratory phase with a slight increase in pressure of the order of 10 to 20 mbar. In the expiratory phase, an expiration valve is opened and the respiratory pressure is reduced to the ambient pressure (PEEP=0). In special cases an artificial increase in pressure in the expiratory phase may also be chosen, i.e. the expiration valve is set at a PEEP p&gt;0, e.g. p (PEEP).apprxeq.2 to 5 mbar.
The anesthetic machines on the market are, as a rule, designed either only for the half-open anesthetic system or only for the half-closed anesthetic system or can be switched between the two systems.
For the ventilation part in the so-called "half-open anesthetic system", either so-called "flow choppers" or so-called "respirators with compressed gas store" are used. A "flow chopper" of this type with controlled expiration valve is depicted in FIGS. 9a and 9b. In this connection, FIG. 9a shows the inspiratory phase and FIG. 9b shows the expiratory phase. The reference numbers used in FIGS. 6 to 8 are also used further for the same parts hereinafter.
In the inspiratory phase shown in FIG. 9a, with the expiration valve 13 closed the patient's lung is filled by the fresh gas 5 which comes through the inspiratory branch 10 from the combined anesthetic apparatus 2 with ventilation machine 3 and high-pressure gas supply. In the expiratory phase shown in FIG. 9b, the patient is able to exhale through the expiration line 7 with the expiration valve 13 open. In this case, the continuous fresh gas flow 5 is, in the expiratory phase, likewise passed out through the expiration valve 13 to the outside or into an anesthetic extractor 8 (arrow 19). Recycling of the expired respiratory gas is not provided for. This system is therefore uneconomic and costly and requires an additional unit for conditioning the inspiratory gas.
There is no reuse of the expired gas from the patient's airway in the known half-open anesthetic system with a respirator with compressed gas store as depicted in FIGS. 10a, 10b. As depicted in FIG. 10a for the inspiratory phase, this anesthetic system has besides the anesthetic apparatus 2 an additional compressed gas store 14 as ventilation part 3 which consists of a fixed plate 15 and a movable plate 16 and of a pressure spring system 17. This half-open anesthetic system additionally has a controllable inspiration valve 18. In the inspiratory phase shown in FIG. 10a, the inspiration valve 18 is open and the controlled expiration valve 13 is closed. When the inspiration valve 18 is open, because of the pressure gradient between the compressed gas store 14 and the patient's lung, the fresh gas 5 flows through the inspiratory branch 10 to the patient. The compressed gas store 14 forming the ventilation machine is filled continuously or intermittently by the high-pressure gas supply of the anesthetic apparatus 2 until the pressure is about 5 bar. Very accurate gas metering is possible with the aid of the controllable inspiration valve 18 and also makes it possible to ventilate neonates. Besides good controllability, this system is distinguished by high gas tightness. However, the disadvantages are the high gas consumption and the lack of conditioning by the half-open anesthetic system because, in the expiratory phase depicted in FIG. 10b with the expiration valve 13 open, the expired respiratory gas is completely lost to the environment or in the anesthetic extractor 8 (arrow 19). During the expiratory phase, the inspiration valve 18 remains closed and the fresh gas 5 flows into the compressed gas store 14 and loads the latter up again against the force of the pressure spring system 17.
Another solution for a "half-open anesthetic system" according to the known system is indicated in FIGS. 11 and 12, with FIGS. 11a, 12a in each case depicting the inspiratory phases and FIGS. 11b, 12b depicting the expiratory phases.
In FIG. 11, a piston pump 20 is used as ventilation part 3 in place of the compressed gas store 14 in FIG. 10. This piston pump 20 is extended in FIG. 12 by the so-called "bag in the bottle" principle whose location is identified by reference number 21. In place of the controllable inspiration valve 18 in FIG. 10, a normal non-return valve 22 is provided in the exemplary embodiment shown in FIGS. 11 and 12.
In the exemplary embodiment shown in FIG. 11a, the piston pump 20 is actuated in the inspiratory phase and forces the fresh gas 5, which is present in the relevant cylinder space, through the automatically opening non-return valve 22 in the inspiration branch 10 to the patient. The controllable expiration valve 13 is closed in this phase. During the expiration phase shown in FIG. 11b, the expiration gas 9' exhaled by the patient flows into the expiration branch 7 and reaches the environment through the opened expiration valve 13 (arrow 19). The inspiration valve 22 in the inspiration branch 10 is closed during this phase. Because the inspiration valve 22 is designed only as non-return valve, the required ventilation pressure can in principle be built up only during the actual inspiration process, whose level depends on the elasticity of the patient's lungs and the flow resistance. However, it is also possible, by retracting the piston inside the piston pump 20, to convey, even during the expiration phase shown in FIG. 11b, part of the fresh gas 5 from the anesthetic apparatus 2 with high-pressure gas supply into the piston pump 20. However, the pressure which is built up in this inspiratory branch must be less than the expiratory pressure in the expiration branch 7 so that the non-return valve 22 remains closed.
The half-open anesthetic system shown in FIGS. 12a, 12b operates in principle in the same manner as described for FIGS. 11a, 11b. In this case, the fresh gas 5 is on each occasion removed or charged from the bellow or bag 23 of the unit 21. The gas flowing out of the piston pump 20 is moreover called the "primary system" inside the container 24, and the gas flowing out of the bag 23 is called the "secondary system".
However, the known system shown in FIGS. 11, 12 with piston pump 20 has considerable disadvantages in practice. The amounts of inspiratory gas required are between 5 ml and 2500 ml depending on the type of patient (infant or baby with a body weight below 2 kg or adult). Moreover, the piston advance of the piston pump 20 is not proportional to the amount of gas conveyed thereby and reaching the patient because, on the one hand, the gas is compressed and, on the other hand, there is further additional supply of fresh gas from the anesthetic apparatus 2. "Loading up" of the system is not possible because of the non-return valve 22 so that the inspiratory branch is subject to virtually no control. Furthermore, there is likewise a high consumption of fresh gas on the basis of the half-open anesthetic system shown in FIGS. 11, 12, associated with a lack of conditioning similar to the embodiment shown in FIGS. 9 and 10.
The known systems shown in FIGS. 11 and 12 can also be designed as so-called "half-closed anesthetic systems". In this case, the connecting line 25, which is drawn in the form of a broken line in FIGS. 11 and 12, is provided between the lower inspiratory branch 10 and the upper expiratory branch 7. An additional non-return valve 26 in the connecting line 25 is closed during the inspiratory phase shown in FIGS. 11a, 12a and open during the expiratory phase 11b, 12b. The expiratory respiratory gas 9' is accordingly able to reach the inspiratory branch 10 via the line 25 from the expiration branch 7 during the expiration phase. This is indicated with the appropriate arrows in FIGS. 11b, 12b. The abovementioned disadvantages with the restriction of an excessive consumption of fresh gas remain even in a half-closed anesthetic system of this type.
Finally, FIGS. 13a, 13b depict a known "half-closed anesthetic system" as has been further developed from the example shown in FIGS. 11a, 11b. In this case, FIG. 13a shows the inspiratory phase and FIG. 13b shows the expiratory phase of the anesthetic system. The difference from the exemplary embodiment shown in FIG. 11 is in the exemplary embodiment shown in FIG. 13 the provision in the expiratory branch of a controllable expiration valve 13 and, additionally, a controllable outlet valve 27. This valve arrangement makes it possible to determine the extent of the expiratory gas to be reused by means of the controllable outlet valve 27. If the outlet valve 27 is completely closed, the anesthetic system changes its function to a "closed anesthetic system" shown in FIG. 8, i.e. the complete expiratory gas 9' reaches the connecting line 25 to the inspiratory branch 10. The extent of the diversion of the expiratory gas is determined according to the degree of opening of the outlet valve 27. Accordingly, in intermediate positions, the anesthetic system is a so-called half-closed one as depicted in principle in FIG. 7. The arrangement depicted in FIGS. 13a, 13b accordingly has control advantages compared with the arrangement shown in FIGS. 11a, 11b. However, the mode of functioning in principle is the same.
The above description of the prior art shows the use in principle of anesthetic systems in the half-open, half-closed or closed modes of operation in each case. In general, this multiplicity of known anesthetic systems generally has the disadvantage that precise control of the inspiratory gas is impossible because even with a controllable inspiration valve 18 according to the known solution shown in FIG. 10, accurate metering and conditioning of the inspiratory gas is impossible. It is true that the fresh gas can be as it were "previously tensioned" by the compressed gas store 14 during the expiratory phase. However, circulation of the expiratory respiratory gas is not provided for in this known system.